<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width,initial-scale=1.0">
  <title>transform-origin</title>
  <style>
    html,
    body {
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      margin: 0 auto;
      height: 100%;
      width: 100%;
    }

    .outer {
      /**定义子元素水平居中**/
      display:flex;
      justify-content:center;
      width: 100px;
      height: 100px;
      background-color: #6a5acd8c;
      position:relative;
    }
    /**竖向辅助线**/
    .vertical-line{
      position:absolute;
      left:50%;
      transform:translateX(-50%);
      height:100%;
      width:1px;
      background:#000;
    }
    /**横向辅助线**/
    .horizontal-line{
      position:absolute;
      top:50%;
      transform:translateY(-50%);
      width:100%;
      height:1px;
      background:#000;
    }
    .inner {
      width:20px;
      height:20px;
      border-radius:50%;
      background-color: #6a5acdeb;
      transform-origin:50% 50px;/**50px为环绕半径*/
      animation:an-circle 3s ease-in-out infinite;
    }
    @keyframes an-circle  {
       to {
          transform: rotate(1turn);
       }
    }
  </style>
</head>
<body>
  <div class="outer">
    <div class="horizontal-line"></div>
    <div class="vertical-line"></div>
    <div class="inner"></div>
  </div>
  <br/>
  <p>圆周环绕动画</p>
</body>
</html>
